It is known to perform single ended line testing (SELT) in digital subscriber lines (DSL). SELT comprises reflectometry-based measurement procedures that allow for determining, at least in some cases, a location of a bridged tap in a subscriber line.
A bridged tap is a branch at the telecommunication line, with the first end of the bridged tap corresponding to a junction point within the telecommunication line. A second end of the bridged tap may be open or connected to a device not belonging to the digital subscriber line. For instance, a bridged tap may be the result of incorrect wiring e. g. in a remote cabinet. A bridged tap can also occur in in-house wiring. For example, a bridged tap can be created by connecting analogue or ISDN telephone equipment to a segment of the telecommunication line connected to a DSL modem without using a DSL splitter to properly separate the frequency bands used for DSL data transmission and telephony from each other.
When operating a telecommunication line having a bridged tap, unwanted reflections may occur at the first end and/or at the second end of the bridged tap in particular when the bridged tap is not correctly terminated at its second end. Because these reflections may disturb DSL data transmissions, it is required to detect and remove a bridged tap.
Known approaches for detecting a bridged tap within a telecommunication line cannot determine a type of the bridged tap. A bridged tap can be of a first type, where the bridged tap has two electrical conductors that are connected to both conductors of a conductor pair of the telecommunication line. In the following, this type of bridged tap will be referred to as “wire pair bridged tap”. Bridged taps of a second type have only one conductor or wire that is connected to one of the two electrical conductors of the telecommunication line. Bridged taps of this second type will further be referred to as “single wire bridged taps”.
When using known approaches for detecting a bridged tap, wire pair bridged taps are typically rather reliably detected. However, single wire bridged taps are much less reliably detected because single wire bridged taps have a smaller impact on the transfer function of the telecommunication line than wire pair bridged taps.